You are looking at it the wrong way. It's not about Facebook's evil end game today. It's about what their current collection of data enables a future Facebook (or a company that may buy Facebook one day) to do. It's also about what malicious actors, government or otherwise, may do with the data if they get their hands on it, as they have, multiple times, in the recent past.

Today the data is used to show you ads. There is no guarantee that it will be used for just that purpose in the future.